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Mozilla Thunderbird CVE-2026-84637

| EUVDEUVD-2026-69703 CRITICAL
Unrestricted Upload of File with Dangerous Type (CWE-434)
2026-09-01 mozilla GHSA-3q74-4f83-x4rj
Red Hat Mozilla File Upload Thunderbird Suse
9.8
CVSS 3.1 · Vendor: mozilla
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Severity by source

Vendor (mozilla) PRIMARY
9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
8.8 HIGH

Remote crafted invite (AV:N/PR:N) but victim must open the invite and activate the attachment (UI:R); successful launch yields full user-context code execution (C:H/I:H/A:H) on Windows.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
SUSE
8.8 HIGH
AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Red Hat
8.8 HIGH
qualitative

Primary rating from Vendor (mozilla).

CVSS VectorVendor: mozilla

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

5
Metadata Corrected
Sep 02, 2026 - 19:40 vuln.today
tag: Microsoft removed
Analysis Generated
Sep 02, 2026 - 19:29 vuln.today
CVSS changed
Sep 02, 2026 - 19:22 NVD
9.8 (CRITICAL)
CVE Published
Sep 01, 2026 - 21:25 cve.org
UNKNOWN (no severity yet)
CVE Published
Sep 01, 2026 - 21:25 cve.org
CRITICAL 9.8

DescriptionCVE.org

Malicious calendar invitations could use file URI attachments to launch local or network-hosted executables on Windows, bypassing Thunderbird's normal executable attachment protections. With the new invitation display enabled, the attachment could also appear under a misleading filename. This vulnerability was fixed in Thunderbird 154 and Thunderbird 153.2.

AnalysisAI

Arbitrary code execution in Mozilla Thunderbird before 154 (and before ESR 153.2) on Windows allows a crafted calendar (iCalendar) invitation to attach a file:// URI that points at a local or network-hosted executable, bypassing Thunderbird's normal blocking of executable attachments. When the new invitation display is enabled the attachment can also be shown under a misleading, benign-looking filename. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Exploit
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Execution
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Vulnerability AssessmentAI

Exploitation Requires the target to run Thunderbird on Windows (the file URI executable-launch behavior is Windows-specific) and to open a malicious calendar invitation and activate/trigger the file URI attachment - so victim interaction is a required precondition. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The vendor CVSS is 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), but that vector is inconsistent with the described attack: launching an executable from a calendar invitation realistically requires the victim to open the invitation and activate/trigger the attachment, which is user interaction (UI:R), and the impact is limited to Windows platforms. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to a fixed build - Vendor-released patch: Thunderbird 154 or Thunderbird 153.2 - as referenced in Mozilla MFSA-2026-78 and MFSA-2026-88. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Identify all Windows systems running Thunderbird versions before 154 or ESR 153.2, and temporarily disable the new invitation display feature in Thunderbird settings to reduce attack surface. …

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Affected
SUSE Linux Enterprise Module for Package Hub 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected

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CVE-2026-84637 vulnerability details – vuln.today
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